1. Field of the Invention
This invention generally relates to an obstacle recognition system for a vehicle. This invention specifically relates to a system including a radar device for scanning a range outside a subject vehicle by a light beam or a radio wave beam, and a recognition device for processing an output signal of the radar device to recognize or detect an obstacle with respect to the subject vehicle.
2. Description of the Prior Art
Some of known obstacle recognition systems scan a given angular range outside a subject vehicle by a light beam or a millimeter radio wave beam. During the scanning process, the beam is emitted into the given range from a transmitter on the subject vehicle, and a reflected or echo beam is received by a receiver on the subject vehicle. An obstacle in the given range is recognized or detected in response to the reception of the reflected beam.
Such an obstacle recognition system is used as a part of a forward obstacle warning system which serves to detect an obstacle such as a preceding vehicle ahead of a subject vehicle and to generate an alarm when there is a possibility of collision between the subject vehicle and the obstacle.
The obstacle recognition system can also be used as a part of a system for detecting the position of a preceding vehicle relative to a subject vehicle, and for automatically controlling the distance between the subject vehicle and the preceding vehicle in response to the detected position of the preceding vehicle.
Japanese published unexamined patent application 5-180933 (corresponding to U.S. Pat. No. 5,291,207) and Japanese published unexamined patent application 5-180934 disclose a system for estimating the position of an obstacle with respect to a subject vehicle which includes a radar device. In the system of Japanese applications 5-180933 and 5-180934, obstacles are detected in response to the reception of reflected beams during a scanning process. Each detected obstacle is represented by a set of equal-area blocks in orthogonal coordinates, and the position of gravity center of the detected obstacle is determined. In addition, the position of gravity center of each detected obstacle is pre-estimated. When the determined position of gravity center of a detected obstacle substantially corresponds to the pre-estimated position of gravity center of a detected obstacle, the obstacles are regarded as a same obstacle.